Oil and gas accumulation conditions and processes of Paleogene in western gentle slope zone of Lufeng 13 east subsag, Lufeng Sag
摘要
Oil and gas exploration practices in the Zhu I Depression of the Pearl River Mouth Basin indicate promising prospects for deep oil and gas resources of the Paleogene in the Lufeng Sag, yet the accumulation conditions and enrichment patterns on the western gentle slope of the Lufeng 13 east subsag remain unclear. To address this issue, well logs, seismic data, and laboratory analyses were integrated with basin modeling to systematically examine the oil and gas accumulation conditions in this area. The oil and gas accumulation conditions and processes were clarified, and oil and gas accumulation models were established. Results showed two oil and gas charging phases in the western gentle slope zone of the Lufeng 13 east subsag: lower-maturity oil charging occurred at 12.3~7.5 Ma (from the mid-Hanjiang to the mid-Yuehai Formation deposition) and oil and gas charging of higher-maturity crude oil mixed with some natural gas occurred at 5.7~0 Ma (from the late Yuehai Formation deposition to the present). The Wenchang Formation developed low-porosity, low-permeability and medium-porosity, medium-permeability reservoirs, while the Enping Formation developed medium-porosity, medium- to low-permeability reservoirs, both offering favorable storage conditions. Two sets of regional mudstone caprocks formed in the Wenchang Formation provided effective sealing for oil and gas. In contrast, the Enping Formation contained multiple sets of local caprocks with relatively weaker sealing capacities. During the first phase of large-scale oil and gas charging, crude oil migrated laterally through Wenchang sandstones to accumulate near the Huilu low uplift. It also migrated vertically along the NW-trending early-inactive faults and continuously active faults into the Enping reservoirs. The second large-scale oil and gas charging phase followed the same migration pathways as those in the first phase. Based on the oil and gas accumulation patterns identified in the study area, two accumulati